and many more benefits!

Find us on Facebook

GMAT Club Timer Informer

Hi GMATClubber!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Show Tags

10 Jul 2016, 02:53

d=(−8)2+4b=0d=(−8)2+4b=0 . Solving for bb gives b=−16b=−16.Not clear as to why we are placing value of a in the above equation.Since equal roots,as per what I understand ,we should be placing the value in this equation.b^2-4ac=0 But I know that there is some other approach to it and I am unclear about that.Please help

Since one of the roots of the equation \(x^2 + ax + 15 = 0\) is 3, then substituting we'll get: \(3^2+3a+15=0\). Solving for \(a\) gives \(a=-8\).

Substitute \(a=-8\) in the first equation: \(x^2-8x-b=0\).

Now, we know that it has equal roots thus its discriminant must equal to zero: \(d=(-8)^2+4b=0\). Solving for \(b\) gives \(b=-16\).

Answer: D

Why you substitute the -8 back into the first equation? what is the relation between the two equations?I know my question might be stupid but I am not getting what they are asking, maybe it´s my english...thanks!!

MBA Acceptance Rate by Undergraduate Major Many applicants may wonder if their undergraduate major impacts their chance of getting into business school. Admissions data suggests that your college major...